Palladium phosphide chalcogenides

ABSTRACT

Crystalline palladium phosphide chalcogenides having the formula PdPSxSe1 x wherein x is from 0 to 1 inclusive can be prepared by heating together stoichiometric amounts of the requisite elements or their binary compounds. These compounds have X-ray diffraction patterns that can be indexed on the basis of similar orthorhombic unit cells. They are semiconductors useful in solid state electronic devices, and also as catalysts for the replacement of aromatic hydrogen with halocarbonyl groups.

United States Patent [191 Bither, Jr.

[451 Sept. 25, 11973 PALLADIUM PHOSPHIDE CHALCOGENIDES [75] Inventor:Tom Allen Bither, Jr., Wilmington.

Del.

[73] Assignee: E. I. Du Pont de Nemours and C0., Wilmington. Del.

[22] Filed: Sept. 12, 1969 [21] App]. No.: 857,562

[56] References Cited UNITED STATES PATENTS 7/l970 Hulliger 23/3l52/l97l Hulliger.... l/l967 Hulliger 23/315 OTHER PUBLICATIONSI-lulliger, Nature, Vol. 198, pages 382-383 (1963).

Primary ExaminerM. Weissman Attorney-D. R. J. Boyd [57] ABSTRACTCrystalline palladium phosphide chalcogenides having the formula PdPS Sewherein x is from 0 to l inclusive can be prepared by heating togetherstoichiometric amounts of the requisite elements or their binarycompounds. These compounds have X-ray diffraction patterns that can beindexed on the basis of similar orthorhombic unit cells. They aresemiconductors useful in solid state electronic devices, and also ascatalysts for the replacement of aromatic hydrogen with halocarbonylgroups.

3 Claims, N0 Drawings PALLADIUM PI-IOSPHIDE CHALCOGENIDES FIELD OF THEINVENTION This invention relates to novel semiconducting inorganiccompounds and more particularly to novel ternary chalcogenides ofpalladium having semiconducting properties.

BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION The compounds ofthe present invention are crystalline palladium phosphide chalcogenideshaving the formula PdPS Se wherein at is from to 1', characterized byX-ray diffraction powder patterns that can be indexed on the basis ofsimilar orthorhombic unit cells and semiconductivity.

DETAILED DESCRIPTION OF THE INVENTION The novel compounds of thisinvention have the formula when x is from 0 to l inclusive, that is, therelative properties of sulfur and selenium can vary continuously fromPdPS to PdPSe, but contain in all cases a stoichiometric proportion ofthe chalcogenide. The products are crystalline and have a crystalsymmetry lower than cubic. The X-ray diffraction powder patterns can allbe indexed on the basis of similar orthorhombic unit cells.

The palladium phosphorus chalcogenides of this invention may be preparedby heating at a temperature of 700-l,300C., preferably at 900-l,OO0C.,and a pressure ranging from autogenous (i.e., less than 200 atmospheres)to 65 kilobars (kbars) in case of PdPS, from autogenous to about 45kbars in case of PdPSe, and from autogenous to about 20 kbars in case ofpalladium phosphide sulfide-selenides, in all cases preferably fromautogenous to 20 kbars, mixtures of the requisite elements and/or theirbinary compounds in, preferably, the approximate stoichiometric ratiocorresponding to that of the desired product.

The time of heating is not critical, but is generally from about minutesto about 2 hours or more.

Commercially available, finely divided, pure elemental forms ofpalladium, phosphorus, sulfur, and selenium are preferred as reactantsthough palladium sulfides, e.g., Pd,S, PdS, PdS palladium selenides,e.g., Pd,Se, Pd,-,Se,,,, PdSe,, palladium phosphides, e.g., PdP PdP andphosphorus sulfides and selenides, e.g., P483, P4810, P485, P487, P2Se3,P2865, may also be em ployed as reactants in conjunction with use ofappropriate quantities of elementary reactants. Quaternary palladiumphosphide sulfide-selenides, PdPS Se may also be prepared by reaction ofPdPS and PdPSe in stoichiometric ratios selected to give desiredcompositions. Use of reactant mixtures in which the stoichiometric ratioof the reactants differs from that of the PdP(S,Se) of the inventionresults in presence of impurities. Impurities may be separated bysolubilization by reaction with water, manually, by dispersion anddecantation, by extraction, etc.

Reaction pressure is particularly important when the reactants are notemployed in the stoichiometry of the product. For example, reaction ofPd:P:S in 1:1:1 atomic ratio gives virtually homogeneous orthorhombicPdPS over the entire autogenous-65 kbar pressure range. In contrast,reaction of these same elements in 1:l: 2 atomic ratio at 600-1,200C.and pressures above about 40 kbars gives little or no orthorhombic PdPS.Although orthorhombic PdPSe forms at 1,000-1,200C. and pressures of 25kbars and lower, little or none appears to be formed at pressures of 45kbars and higher.

Single crystal studies of the PdPS of this invention show that it hasorthorhombic crystal symmetry. Chemical analyses, density measurements,and measured orthorhombic cell dimensions show that the unit cellcontains 8 molecules of PdPS. A unique composition, i.e., essentially norange of stoichiometry, is shown by the fact that the unit celldimensions are the same for prod ucts prepared at pressures ranging fromautogenous to 65 kbars. In addition, variations in the ratio of startingmaterials, which still give this orthorhombic phase as one of theproducts of the reaction, do not lead to a variation in the unit celldimensions. As with PdPS, variations in reaction pressure and in theratio of components employed in the Pd-P-Se reaction lead to PdPSe ofthe same unit cell dimensions, suggesting that it, like PdPS, haslittle, if any, range in compositional stoichiometry.

Like PdPS, PdPSe and quaternary PdPS Se compositions give X-ray powderpatterns that can be indexed on the basis of similar orthorhombic unitcells. Although the X-ray diffraction powder patterns appear to be thoseof isotypic compounds, a few relatively weak but indexable reflectionsappear in the patterns of Se-containing compositions that do not fitinto the space group requirements established for PdPS. For this reason,it is not possible to state unequivocally that all the compositions ofthe invention are isotypic though all are indexable on the basis ofsimilar orthorhombic unit cells.

The products of the invention may be prepared in any suitably chemicallyinert reaction vessel capable of withstanding the pressure developed orapplied during reaction. When the reaction is conducted at autogenouspressure, it is convenient to seal the reactants under vacuum inthick-walled quartz tubing and to heat the tubes containing thereactants in a pressure vessel to which 200 atmospheres of argon isapplied as a counter-balancing pressure to prevent rupture of the quartztubes by internally developed pressure during heating. The pressurevessels in which the charged, evacuated, and sealed quartz tubes areplaced may be heated internally, e.g., by electrical means. Anespecially useful type of pressure vessel is an argonpressured bomb,capable of being heated to 1,400C. by an internal platinum resistanceheater. Sealed quartz tube reactors may be used at temperatures as highas 1,350C. with a back-up pressure of 3 kbars to prevent rupturing.

The time of heating at maximum temperature is not critical and 0.25 hourto 2 hours is usually adequate.

The rate of cooling after reaction is not critical though gradualreduction in temperature at a rate of about 25200C. per hour until theproduct has solidified usually favors increase in the crystallite sizeof the product. Optionally, the temperature may be lowered very rapidlyto room temperature in a matter of a few seconds, a procedure referredto hereinafter as quenching. Pressure may be allowed to drop withtemperature, as in case of reactions carried out at autogenous pressure,or maintained until the product reaches room temperature, as in case ofreactions conducted in the tetrahedral anvil.

Reactions at pressures greater than 3 kbars are conveniently carried outin a tetrahedral anvil pressure device as described by E. C. Lloyd, etal., Jour. of Research, National Bureau of Standards 63C, 59 (1959). Inthis device, the reactants are placed in a boron nitride container whichfits in a graphite sleeve that serves as a resistance heater. Thisassembly is enclosed in a pyrophyllite tetrahedron and is placed in theanvil device which is capable of generating pressures in excess of 65kbars. The four calibration points used to determine pressure developedin this device appear in the 1963 edition of the American Institute ofPhysics Handbook, Part 4, p. 43, as follows:

Bismuth I 11 25.37 i 0.02 kbars Bismuth 11 111 26.96 i: 0.18 kbarsThallium II 111 36.69 i 0.11 kbars Barium II 111 59.00 i 1.0 kbars Allcompressions are made on the cold assembly and the charges are thenheated to the desired temperature using an appropriate thermocouple. Nopressure correction for thermocouple behavior has been introduced,standard e.m.f. tables for 1 atmosphere being employed. The pressureunit is a bar, equivalent to dynes/cm The larger unit, a kilobar (kbar),equal to 1,000 bars is used herein.

A preferred method of carrying out the process of this inventioninvolves mixing equiatomic quantities of palladium, phosphorus, andchalcogen, said chalcogen being selected from sulfur and/or selenium,sealing the mixture in a heavy-walled, evacuated quartz tube which isplaced in an electrically heated pressure vessel, applying a backuppressure of 200 atmospheres of argon, and heating in about 1 hour toapproximately 900C. The reaction mixture is held at 900C. for about .2hours, then gradually cooled over a 3-hour period to 400-600C., andfinally cooled to room temperature by discontinuing heating. Theresulting palladium phosphide chalcogenide is removed from the quartztube, extracted with water to remove hydrolyzable phosphoruschalcogenide impurities and, if desired, with carbon disulfide todissolve unreacted sulfur, washed with acetone to facilitate drying, anddried. The thus-formed palladium phosphorus chalcogenides are gray tosilvery in appearance.

SPECIFIC EMBODIMENTS OF THE INVENTION This invention is furtherillustrated by the following examples in which parts and percentages areby weight unless otherwise stated.

EXAMPLE 1 Reaction of Pd:P:S in a 1:1:1 atomic ratio at a pressure of 65kbars and a temperature of 1,200C.

A 0.623-g. pellet from a mixture of 0.745 g. of Pd, 0.217 g. of P, and0.224 g. of S was pressured to 65 kbars in a tetrahedral anvil andheated to 1,200C. in 1 hour, held 1 hour at 1,200C., cooled over a4-hour period to 400C, and quenched to room temperature. This gave adense slug of product that could be fractured into crystals of laminarhabit that were metal-like in color. X-ray precession photographs takenon single crystals showed that the material had orthorhombic symmetry(space group P2 ca or Pmca) with cell dimensions a= 5.69, 12 13.33, c568A. The X-ray diffraction powder pattern obtained upon these crystalswith a H'agg-Guinier camera using monochromatic Cu radiation and a KClinternal standard (a 6.2931A) is given in Table I:

TABLE I X-Ray Diffraction Powder Pattern of PdPS Intensity hkl dSpacing, A 5 020 6.6500 15 011 5.2171 100 111 3.8465 20 121 3.4413 15040 3.3250 5 131 2.9773 5 200 2.8443 50 002 2.8380 210 2.7826 5 2202.6167 50 211 2.4981 50 112 2.4948 10 230 2.3975 5 122 2.3739 10 0422.1591 10 202 2.0099 75 212 1.9873 5 232 1.8310 75 113 1.7798 50 3211.7376 20 123 1.7341 2 133 1.6648 15 302 1.5777 2 213 1.5648 2 2621.4895 2 400 1.4235 5 004 1.4194 20 323 1.3138 5 144 1.2725 10 4121.2665 15 214 1.2646

An intensity value of is assigned to the strongest line of the pattern.

This X-ray diffraction powder pattern can be indexed on the basis of anorthorhombic unit cell with a 5.693, b 13.305, c 5.687A (unit cellvolume 430 A in agreement with the results of the single crystal X-raymeasurements.

A second sample of this material was prepared in the same manner aspreviously described and, following extraction with carbon disulfide andthen acetone, was observed to have the same X-ray diffraction powderpattern as that given in Table l. Elemental analyses for Pd, P, and Sindicated these to be present in the atomic ratio Pd:P:S l.00:l.00:l.10,which within the limits of experimental error correspond to PdPS. ThePdPS was found to have a measured density of 5.13 g/cm From the volumeof the orthorhombic unit cell (430 A), the molecular weight (169.4) andthis measured density, 8 formula weights per unit cell are indicated,i.e., n 7.84 (see Introduction to Solids, L. V. Azaroff, McGraw-Hill,1960, pp. 53, 54).

Four probe resistivity measurements on a single crystal of the PdPSphase showed it to be a semiconductor with resistivities p K 9 X 10 andp K 3 X 10' ohm-cm and an activation energy of resistivity, Ea, of 0.7eV. This material, on exposure to ultraviolet, visible, or infraredradiation, showed a modest degree of photoconductivity, as noted by adecrease tance (Example B).

Optical transmission was measured on a crystal platelet, and a band edgenear a wavelength of 0.9 1. was observed, indicating an optical bandgap, AE, of about 1.38 eV. This value is in excellent agreement with theactivation'energy of resistivity, Ea 0.7 eV, reported above (Ea isidentical to AE/2). The geometry of the crystal platelet used in theoptical measurements was such that the refractive index, n, ofPdPS'could also be determined from the same data. A value of n between3.1 and 3.6 was calculated.

Magnetic susceptibility measurements showed that the PdPS wasdiamagnetic.

EXAMPLE 2 Reaction of Pd:P:S in a l:l:1.5 atomic ratio at a pressure of40 kbars and a temperature of 1,000C.

A 0.550-g. pellet from a mixture of l.l70 g. of Pd, 0.341 g. of P, and0.529 g. of S was pressured to 40 kbars in a tetrahedral anvil, heatedfor 2 hours at l,000C., gradually cooled over a 4-hour period to 400C,and quenched to room temperature. Most of in its resisthis productconsisted of silvery crystals. Following extraction with water andacetone and drying, the Debye- Scherrer X-ray diffraction powder patternof the product was the same as that of Example 1 (Table I) except forfour extra weak diffraction lines, perhaps arising from a minor amountof PdS impurity, formed as a consequence of the stoichiometric excess ofS used as a' reactant. Equivalence of the unit cell sizes of PdPSprepared from stoichiometric (Example 1) and nonstoichiometric (thisexample) amounts of starting material and over a range of pressure from65 kbars to autogenous (Examples 14), is indicative of an essentiallyconstant P/S ratio in PdPS.

The PdPS produced in this example catalyzed the replacement of aromatichydrogen in benzene with halocarbonyl, thus leading to the formation ofbenzoyl chloride (Example A).

EXAMPLE 3 Reaction of Pd:P:S in a 1:1:1 atomic ratio at a pressure of 3'kbars and a temperature of 1,200C.

A mixture of 0.316 g. of Pd, 0.092 g. of P, and 0.095 g. of S in powderform was sealed under vacuum in heavy walled, quartz tubing. The-sealedtube was then v heated for 2 hours at 1,200C. under an external argonargon in a differential thermal analyzer. it was stable up to about-800C., at which temperature heat was absorbed and decomposition tookplace.

EXAMPLE 4 Reaction of Pd:P:S in a l:l:l atomic ratio at autogenouspressure and a temperature of 900C.

A mixture of 0.358 g. of Pd, 0.104 g. of P, and 0.107 g. of S in powderform was sealed under vacuum in quartz tubing. The tube was heated for 2hours at 900C. under an external back-up pressure of argon of 200atmospheres, and cooled over a 3-hour period to 600C, whereupon heating.was stopped. The product consisted of a gray powder containing a smallamount of tiny, silvery, plate-like crystals. This product was extractedwith aqueous acetone and dried in air. Debye- Scherrer X-ray diffractionpowder patterns upon both the'powder and small crystals were identicalto that of the product of Example 1 (Table l), indicating thesematerials to be PdPS.

EXAMPLE 5 Reaction of PdzPzSe in a 1:121 atomic ratio at autogenouspressure and a temperature of 900C.

A mixture of0.340 g. of Pd, 0.0991 g. of P, and 0.253 g. of Se wassealed under vacuum in quartz tubing. Reaction was effected at 900C. inthe manner described in Example 4. The resulting product consisted of anelongated silvery mass which had a Debye-Scherrer X-ray diffractionpowder pattern (Table II) that could be indexed on the basis of anorthorhombic unit cell with a 5.856, b= 13.569, c 5.824 A (unit cellvolume 463 A TABLE II X-ray Diffraction Powder Pattern of PdPSeintensity in k I dSpacing,A 1 1 1 3.9515 20 0 3 1 3.5680 100 0 4 03.3980 10 1 3 1 3.0475 55 0 0 2 2.9131 2 1 0 2.8621 30 0 5 1 2.7127 20 22 0 2.6932 35 1 4 1 2.6199 1 1 2 2.5633 25 2 3 0 2.4571 35 .2 3 1 2.265325 0 4 2 2.2103 2 2 4 1 2.0697 30 2 1 2 2.0407 10 2 5 0 1.9895 5 3 0 01.9497 50 1 5 2 1.8795 40 1 1 3 l.8263 s5 0 3 3 1.7843 15 1 6 2 1.7089 52 5 2 1.6427 15 3 0 2 1.6218 15 3 1 2 1.6098 15 1 8 1 1.5693 20 2 6 21.5249 5 4 0 0 1.4643 20 4 2 0 1.4311 15 1 9 1 1.4155 5 3 5 2 1.3914 5 07 3 1.3731 5 1 3 4 1.3475 5 2 0 4 1.3041 5 1 5 4 1.2541 5 0 10 2 1.22965 2 4 4 1.2171 5 1 9 3 1.1669 5 4 7 1 1.1446 10 0 3 5 l.l280 2 5 3 11.1127 5 1 4 5 1.0828 5 0 5 5 1.0702 5 5 3 2 1.0562. 5 1 9 4 1.0303 5 113 1 1.0127

An intensity of is assigned to the strongest line of the pattern.

Elemental analyses of the material indicated the atomic-ratio of Pd:P:Seto be 1.00:1.04:0.94, which within the limits of experimental errorcorresponds to the formula PdPSe.

EXAMPLE 6 Reaction of Pd:P:Se. in a 1:111 atomic ratio at a pressure of20 kbars and a temperature of l,000C.

A 0.699-g. pellet from a mixture of 1.278 g. of Pd, 0.373 g. of P, and0.948 g. of Se was pressured to 20 kbars in a tetrahedral anvil andheated for 2 hours at l,000C., cooled over a 4-hour period to 400C, andquenched toroom temperature. A dense slug of product was obtained thatupon fracture gave silvery, bladelil te crystals at the sample ends. TheDebye-Scherrer X-ray diffraction powder pattern of these crystals wasthe same as that of the product of Example 5, indicating them to'bePdPSe. I

Crystals of PdPSe were isolated from asecond run in which conditionswere similar to those used to obtain the material described above. Thesecrystals had the same Debye-Scherrer X-ray diffraction powder pattern ofExample 5. Four probe resistivity measurements made on one of thesecrystals of PdPSe showed it to be a semiconductor with resistivities p K4 X p 4 30, p K l ohm-cm and an activation energy .of resistivity, Ea,of 0.15 eV over the temperature 8 Paoo-4ook.

EXAMPLE 7 Reaction of Pd:P:Se in a 1:0.67: l.33 atomic ratio at apressure of 25 kbars and a temperature of l,000C. A 0.719-g pellet,pressed from a mixture of 1.277 g. of Pd, 0.248g. of P, and 1 .263 g. ofSe, was pressured to 25 kbars in a tetrahedral anvil and was then heatedEXAMPLE 8 Reaction of PdzPzSzSe in l:l:0.75:0.25 atomic ratio at apressure of 20 kbars and a temperature of l,000C.

A 0.605-g pellet from a mixture of 0.532 g. of Pd, 0.155 g. of P, 0.120g. of S, and 0.099 g. of Se was reacted in the manner of Example 6.Silvery, blade-like crystals mixed with a minor amount of yellow-brownpowder were formed. A Debye-Scherrer X-ray diffraction powder patternwas obtained upon this product (Table III), and 35 of the 39 observeddiffraction lines could be indexed on the basis of an orthorhombic unitcell with a 5.738, b 13.499, 0 5.698 A (unit cell volume 441 A).Assuming a Vegards rule relationship (see "Concise Chemical andTechnical Dictionary, H.

' Bennett, Chemical Publishing Co., 1962) between the unit'cell volumesofthe end members PdPS,- V 430 A (Example I), and PdPSe, V 463 A(Example 5), the volume of the unit cell of the material of this Example(441 A") indicates the approximate composition PdPS,,,. Se which is inrelatively good agreement with the initial reaction charge. The fourunindexed diffraction lines are attributed to the presence ofunidentified, extraneous material.

and cooled inthe manner of Example 6. The product "An intensity value of100 is assigned to TABLE 111 X-ray Diffraction Powder Pattern of PdPS SePhase Intensity h k I dSpacing,A 15 0 2 0 6.7350 5 0 1 1 5.2507 5 1 2 04.4208 7s 1 1 1 3.8858 5 3.7416 30 1 2 1 3.4689 100 0 4 0 3.3684 25 1 31 7 3.0010 0 o 2 2.8528 50 2 1 0 2.8014 40 0 5 0 2.7155 10 1 4 1 2.594925 2 1 1 2.5252 25 2 3 0 2.4156 35 1 s 1 2.2389 35 0 4 2 2.1764 20 2 0'2 2.0191 25 2 1 2 1.9999 15 0 5 2 1.9529 10 '3 1 0 1.8912 20 2 5 11.8616 25 2 3 2 1.8434 40 1 1 3 1.7892 60 2 6 0 1.7715 7o 0 3 3 1.7487 5-3 3 1 1.6784 2 1.6067 5 1.5126 5 2 33 1.4951 15 4 2 0 1.4036 2 0 3 41.3582 5 3 2 3 1.3215 5 2 0 4 1.2761 5 011 0 1.2273 2 -1 1o 2 1.1920 2 28 3 1.1549 2 1.1335 10 1 0 5 1.1178 5 012 1 1.1034

the strongest line of the pattern.

EXAMPLEQ.

Reaction of PdzPzSzSe in a l:1-:0.5:0.5 atomic ratio at a pressure of 20kbars and a'temperature of l,000C.

A 0.635-g. pellet from a mixture of 0.500 g. of Pd, 0.146 g. of P, 0.075g. of S, and 0.186 g. of Se was reacted in the manner of Example 6.At'the sample ends, granular material was formed, and a Debye-ScherrerX-ray diffraction powder pattern was obtained thereon. The majority ofthe diffraction lines of this pattern could be indexed on the basis ofan orthorhombic unit cell with a 5.755, b 13,544, c 5.722 A (unit cellvolume 446 A). In the manner of Example 8, use of Vegards rule indicatesthe approximate composition PdPS -,Se in agreement with the reactioncharge.

EXAMPLE 10 Reaction of PdzPzSzSe in a 1:1:0.25:0.7S atomic ratio at apressure of 20 kbars and a temperature of 1,0009C.

A 0.66l-g. pellet from a mixture of 0.532 g. of Pd, 0.155 g. of P, 0.040g. of S, and 0.296 g. of Se was reacted in the manner of Example 6. Asin Example 9, granular material was formed at the sample ends and aDebye-Scherrer X-ray diffraction powder pattern was obtained thereon.All diffraction lines of this pattern could be indexed on the basis ofan orthorhombic unit cell with a 5.788, b 13.540, 0 5.770 A (unit cellvolume 452 A). In the manner of Example 8, the use of Vegards ruleindicates the approximate composition PdPs, ,,,se,,,-,, which is inrelatively good agreement with the initial reaction charge.

As described in Examples 1 and 6, the palladium phosphide chalcogenidesof this invention exhibit semihalocarbonyl, thus leading to theformation of aroyl halides.

EXAMPLE A Benzene (75 g.) and carbon tetrachloride (50 g.) in thepresence of a catalytic quantity (0.3 g.) of PdPS, prepared in themanner of Example 2, were charged into a 400 cc. Hastelloy C pressurereactor which was then pressured with 300 atmospheres of carbonmonoxide. This reactor, which was run as a closed bomb, was then heatedfor 4 hours at 300C. Reaction took place to give an 82.5 percentconversion to benzoyl chloride based upon carbon tetrachloride charged.

As shown below inExample B, PdPS is also a photoconductor and is thususeful for making electronic instruments such as light meters, lightsensitive switches and the like.

EXAMPLE B A 220 X 135 X 5-micron platelet of PdPS, prepared by themethod of Example 1, was connected in series with an ohm meter. The darkresistance of the material was 2 X l0 ohms. Upon illumination of theplatelet with an incandescent light (broad visible and infraredspectrum), the resistance dropped to L9 X 10 ohms. By the use ofappropriate radiation sources and filters, the PdPS platelet was exposedto radiation from selected regions of the spectrum, and loweredresistances were observed as follows:

Radiation (A. Resistance (Ohms) 3650 4.6 X 10 4300 2.5 X 10 546] 2.2 X10 3000 3 X 10 Dark 2 X 10 The variation in resistance of this materialwhen exposed to radiation of different wavelengths thus permits thematerial to be used as a detector of radiation.

Similar results can be obtained if the PdPS is replaced with PdPSe orthe compound PdPS Se in Example B above.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A composition having the formula wherein x is from 0 to l inclusive,characterized by semiconductivity, and when x is 1 having the X-raypowder pattern of Table I, and when x is 0 having the powder pattern ofTable ll, and each having an X-ray powder pattern which can be indexedon the basis of similar orthorhombic unit cells.

2. A compound of claim 1 having the formula PdPS characterized bysemiconductivity and having the X-ray powder pattern of Table l.

3. A compound of claim 2 having the formula PdPSe characterized bysemiconductivity and having the X-ray powder pattern of Table II.

2. A compound of claim 1 having the formula PdPS characterized bysemiconductivity and having the X-ray powder pattern of Table I.
 3. Acompound of claim 2 having the formula PdPSe characterized bysemiconductivity and having the X-ray powder pattern of Table II.